The present invention relates to a viscosity detector using an electromechanical vibrator which comprises piezoelectric ceramic members, for example, and vibrates about its central axis, and has a detector member which is immersed in liquid to measure the viscosity thereof and which is vibrated about its central axis, which central axis is coaxial with the central axis of the electromechanical vibrator, via the electromechanical vibrator to measure the viscosity of the liquid based on viscous resistance offered by the liquid.
The present inventors conducted studies on a viscosity detector and conceived a method of measuring the viscosity of liquid by using an electromechanical vibrator, connecting the vibrator to a detector member, immersing the detector member within the liquid, transmitting the vibration of the vibrator to the detector member, detecting viscous resistance offered by the liquid and converting the viscous resistance into an equivalent electric signal. In accordance with their idea, they tried to use a commercially available vibrator vibrating in the direction of its thickness as the electromechanical vibrator. As a result, it was found that the vibrator connected to a detector member caused the detector member to be vibrated vertically relative to the surface of liquid, thereby producing vibration waves propagating within the liquid and thus making it difficult to measure the viscosity of the liquid with a high degree of precision. In view of this, they used a vibrator member having a small wall thickness and tried to vibrate it in a direction parallel to the surface thereof. As a result, however, it was found that it was difficult to vibrate the vibrator member while in a state of being held precisely parallel to the surface thereof due to deviation in the center thereof produced during the operation of the vibration, that the problem of the generation of wave motion was insufficiently solved, that restrictions were present with respect to the surface area of the detector member, to the sensitivity of the detector member to the viscous resistance and to the range of viscosity measurement and therefore that it was difficult to measure the viscosity with a high degree of precision. The inventors have come to a conclusion that the detector member should be stably vibrated within the liquid while the liquid is maintained in a state as static as possible.